Projection tv set apparatus

ABSTRACT

A lens device which is applied to a projection type image display apparatus includes an outer tube and an inner tube forming a tube structure having an optical lens and a thermal react material such as bimetallic sheet disposed between the outer tube and the inner-tube. Lens focus is corrected by moving a relative position between the outer tube and the inner tube in an optical axis direction to thereby maintain an initially set focus position to obtain an image of high picture quality.

This is a division of application Ser. No. 08/397,924 filed Mar. 3,1995, now U.S. Pat. No. 5,617,259.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens focus correction device for usewith a projection type image display apparatus or the like.

2. Description of the Related Art

As a projection type image display apparatus, there has hitherto beenknown a projection type television receiver, i.e., so-called rearprojector in which an image obtained from a cathode ray tube isprojected onto a transparent type screen from the rear surface of thescreen in an enlarged scale.

FIG. 1 of the accompanying drawings shows a schematic arrangement of therear projector. In FIG. 1, reference numeral 1 depicts a cabinet andreference numeral 2 depicts a three-tube color cathode ray tube 2 (2R,2G, 2B) corresponding to red (R), green (G) and blue (B) disposed withinthe cabinet 1. An image from the color cathode ray tube 2 is magnifiedby a projection lens 3, reflected by a reflection mirror 4 and thenprojected onto a front screen 5 from the rear surface thereof.

FIG. 2 shows an example of the rear projector cathode ray tube 2 towhich the projection lens 3 is integrally attached. The cathode ray tube2 uses a liquid-cooling tube in which liquid-cooling liquid 8 is filledinto a space formed by a panel front surface, a curvature of fieldcorrection lens 7 and a sealing frame 9. A tube 10 constructing theprojection lens 3 is fixed to the sealing frame 9 of the liquid-coolingliquid 8 by some suitable means, such as screws 11 or the like.

The tube 10 is composed of an outer tube 12 and an inner tube 13rotatably disposed within the outer tube 12 so that the inner tube 13can be moved along an optical axis. The inner tube 13 has a plurality ofoptical lenses 15, 16 and 17 arrayed therein. In this example, the fouroptical lenses 15, 16, 17 and 7 constitute a projection lens, i.e., mainlens group 3.

The outer tube 12 has on its outer peripheral wall portion an obliquegroove, i.e., oblique guide slot 18 defined with a predetermined anglerelative to an optical axis C from a plane standpoint. The inner tube 13has a guide member 19 integrally extended therefrom. The guide member 19is engaged with the oblique guide slot 18.

The guide member 19 has a thumbscrew 22 fitted thereto through a spacer23 in order to fix the inner tube 13 after the inner tube 13 was set ata predetermined position with respect to the optical axis C direction.

The inner tube 13 has on its front and rear ends disposed slidingportions 20 to come in contact with the inner peripheral surface of th,aouter tube 12 to thereby slidably support the inner tube 13.

The outer tube 12 and the inner tube 13 are each made of plastics(resin).

In this tube 10, when the initial focus position of the main lens group3 is set, initially, the thumbscrew 22 is loosened and the guide member19 is moved along the oblique guide slot 18, whereby the inner tube 13is displaced in the optical axis C direction while the inner tube 13 isbeing rotated with respect to the outer tube 12, thus to adjusting thelens focus position. After the lens focus position has been adjusted,the inner tube 13 is fixed to the outer tube 12 at that position bymeans of the spacer 23.

In the above-mentioned rear projector, a heat generating source, such asthe cathode ray tube 2 and peripheral circuit portions and the opticalsystem, such as lens or the like, i.e., the tube 10, are disposed closeto each other. Thus, as shown in FIG. 3, as a temperature of the rearprojector equipment rises after the cathode ray tube set has beenenergized, respective portions (the tube 10 including the lens system orthe like) expand so that the initial focus position of the main lensgroup 3 is changed which deteriorates an image.

As a means for correcting the lens focus position changed due to a riseof temperature, there is the following method. According to this method,when a lens is designed, a plastic lens whose volume changing ratio witha temperature is large is divided by a plurality of plastic lenses toweaken an optical power (i.e., refracting power) per plastic lens and anoptical power of a glass lens whose volume changing ratio is small isstrengthened to thereby suppress the amount in which the focus positionis changed. As examples of the above-mentioned technique, there aredesign methods disclosed in U.S. Pat. No. 4,776,681, Japanese laid-openpatent publication No. 61-205909 and SID, 1/1, 1933 (A46-in,high-resolution rear-Projection display) or the like.

In the example shown in FIG. 2, in the main lens group comprised of thefour lenses, most of positive power of the optical system is produced bythe second optical lens, i.e., the glass lens 16 of which the volumechanging ratio is small, thereby decreasing the optical powers of thethird and fourth optical lenses 15, 17 and 7 made of plastics.

However, even though the volume changing ratio of the lens itself isreduced, most of the tube 10 for supporting the lenses is made of aresin material and the change of the focus position due to the volumechange of the tube 10 was never taken into consideration.

In the case of FIG. 2, the outer tube 12 provided between the cathoderay tube 2 and the guide member 19 is thermally expanded due to the riseof temperature so that the main lens group 3 is moved to the left-handside direction in FIG. 2. As a result, the focus is displaced from theinitial focus position and an image is deteriorated.

OBJECTS AND SUMMARY OF THE INVENTION

In view of the aforesaid aspect, it is an object of the presentinvention to provide a lens focus correction device which is able tocorrect a lens focus position changed due to a temperature change in thedevice in which an optical lens system is disposed close to a heatgenerating source.

In a lens focus correction device according to the present invention,thermal react materials such as bimetallic sheet are disposed between anouter tube and an inner tube composing optical lenses. This lens focuscorrection device can correct a lens focus by moving a relative positionbetween the outer tube and the inner tube with respect to the opticalaxis direction by the thermal react materials such as bimetallic sheet.

According to the present invention, there is provided a lens focuscorrection device in which slant guide slots are defined on an outerperipheral wall portion of the outer tube with an inclination relativeto the optical axis and in which a rotational displacement of the innertube is converted by the oblique guide slots to the optical axisdisplacement.

According to the present invention, there is provided a lens focuscorrection device in which a thermal react material such as bimetallicsheet is disposed in the optical axis direction or in the direction nearthe optical axis, one end of the thermal react material such asbimetallic sheet is fixed to a slide portion provided on the outer tubeand the other of the thermal react material such as bimetallic sheet isassociated with a guide member integrally formed with the inner tube.

According to the present invention, there is provided a lens focuscorrection device in which a thermal react material such as bimetallicsheet is disposed along an inner peripheral direction of an outer tube,one end of the thermal react material such as bimetallic sheet is fixedto a slide portion provided in the outer tube and the other end of thethermal react material such as bimetallic sheet is associated with aguide member integrally formed with the inner tube.

According to the present invention, there is provided a lens focuscorrection device in which a thermal react material such as bimetallicsheet is formed as a U-letter shape, a guide slot is defined on an outerperipheral wall portion of an outer tube, one end of the thermal reactmaterial such as bimetallic sheet is fixed to a slide portion providedon the guide slot and the other end of the thermal react material suchas bimetallic sheet is associated with a guide member integrally formedwith an inner tube which is engaged with the guide slot.

According to the present invention, there is provided a lens focuscorrection device in which two parallel guide slots are defined on anouter peripheral wall portion of an outer tube, a slide portion isdisposed on one guide slot and a guide member integrally formed with aninner tube is engaged with the other guide slot to thereby keep aneffective operation length of a thermal react material such asbimetallic sheet constant.

According to the present invention, there is provided a lens focuscorrection device in which two guide slots which are not parallel toeach other are defined on an outer peripheral wall portion of an outertube, a slide portion is disposed in one guide slot and one guide memberintegrally formed with the inner tube is engaged with the other guideslot so that an effective operation length of the thermal react materialsuch as bimetallic sheet can be adjusted based on the positions of theslide portions disposed within the guide slots.

According to the present invention, the lens focus correction devicehaving two guide members and in which the other end of a thermal reactmaterial such as bimetallic sheet is sandwiched between the two guidemembers.

According to the present invention, there is provided a lens focuscorrection device in which two guide slots are defined on an outerperipheral wall portion of an outer tube, a slide portion is disposed inone guide slot and a guide member integrally formed with an inner tubeis engaged with the other guide slot.

According to the present invention, there is provided a lens focuscorrection device in which positions at which thermal react materialssuch as bimetallic sheet are fixed to a slide portion can be adjusted toenable effective operation lengths of the thermal react materials suchas bimetallic sheet to be adjusted continuously.

According to the present invention, there is provided a lens focusposition correction device in which thermal react materials such asbimetallic sheet are formed of bimetals.

According to the present invention, there is provided a lens focusposition correction device in which optical lenses are held within aninner tube.

According to the present invention, since the thermal react materialssuch as bimetallic sheet are disposed between the outer tube and theinner tube and the relative position between the outer tube and theinner tube relative to the optical axis direction is moved by thethermal react material such as bimetallic sheet, if the lens focusposition is changed as the tube expands and contracts due to thetemperature change, the inner tube is moved in the opposite directionrelative to the outer tube by the thermal react material such asbimetallic sheet energized due to the temperature change and the lensfocus position is returned to the initial focus position, thereby thefocus position is corrected.

According to the present invention, since the oblique guide slots aredefined on the outer peripheral wall portion of the outer tube with theinclination relative to the optical axis and the rotational displacementof the inner tube is converted into the optical axis directiondisplacement by guiding the inner tube by the oblique guide slots, whenthe thermal react material such as bimetallic sheet are changed, theinner tube is displaced in the optical axis direction while beingrotated to thereby correct the focus position.

According to the present invention, since the thermal react materialsuch as bimetallic sheet is disposed along the optical axis direction orin the direction close to the optical axis direction, one end of thethermal react material such as bimetallic sheet is fixed to the slideportion provided on the outer tube and the guide member integrallyformed with the inner tube is associated with the other end of thethermal react material such as bimetallic sheet, when the focus positionis changed due to the temperature change, the other end of the thermalreact material such as bimetallic sheet is displaced in the directioncrossing the optical axis, whereby the inner tube is displaced along theoptical axis direction in the opposite direction through the guidemember while being rotated, thereby the focus position is corrected.

According to the present invention, since the thermal react materialsuch as bimetallic sheet is disposed along the inner peripheraldirection of the outer tube, one end of the thermal react material suchas bimetallic sheet is fixed to the slide portion provided in the outertube and the other end of the thermal react material such as bimetallicsheet is associated with the guide member integrally formed with theinner tube, when the focus position is changed due to the temperaturechange, the other end of the thermal react material such as bimetallicsheet is displaced in the circumferential direction of the outer tube,whereby the inner tube is displaced along the optical axis in theopposite direction through the guide member while being rotated, therebythe focus position is corrected.

Further, since the thermal react material such as bimetallic sheet isdisposed along the inner peripheral direction of the outer tube, theeffective operation length of the thermal react material such asbimetallic sheet can be increased and action force given to thedisplacement amount of the other end of the thermal react material suchas bimetallic sheet and the guide member can be increased.

According to the present invention, since the thermal react materialsuch as bimetallic sheet is formed as the U-letter shape, the guide slotis defined on the outer peripheral wall portion of the outer tube, oneend of the thermal react material such as bimetallic sheet is fixed tothe slide portion disposed in the guide slot and the other end thereofis associated with the guide member integrally formed with the innertube which is engaged with the guide slot, when the focus position ischanged due to the temperature change, the other end of the thermalreact material such as bimetallic sheet is displaced along thecircumferential direction of the outer tube, whereby the inner tube isdisplaced along the optical axis direction in the opposite directionthrough the guide member while being rotated, thereby the focus positionis corrected.

Further, since the thermal react material such as bimetallic sheet isshaped in U-letter, the effective operation length of the thermal reactcharacteristic can be increased and the displacement amount of the otherend of the thermal react material such as bimetallic sheet can beincreased.

According to the present invention, since the two parallel guide slotsare defined on the outer peripheral wall portion of the outer tube, theslide member is disposed in one guide slot and the guide memberintegrally formed with the inner tube is engaged with the other guideslot, even when the guide member 40 and the slide portion 41 are bothmoved within the guide slots 37, 38 by the adjustment of the initialfocus position, as shown in FIG. 4 it is possible to keep the effectiveoperation length of the thermal react material such as bimetallic sheetconstant at any position in which the guide member and the slide memberare moved. Therefore, the predetermine correction amount by the thermalreact material such as bimetallic sheet can be maintained.

Further, it is possible to set the correction amount to be constantregardless of the projection magnification.

Specifically, when the projection magnification is constant orprojection magnification lies in a narrow projection magnificationrange, the correction amount is not changed depending on the adjustmentposition and therefore the lens focus correction device of the presentinvention is easy to handle.

According to the present invention, since the two guide slots which arenot in parallel to each other are provided on the outer peripheral wallportion of the outer tube, the slide portion is disposed on one guideslot and the guide member which is integrally formed with the inner tubeis engaged with the other engagement hole, it becomes possible to adjustthe effective operation length of the thermal react material such asbimetallic sheet by the positions of the slide portion and the guidemember disposed within the guide slots. Therefore, when the projectionmagnification is adjusted by displacing the inner tube along the guideslots in the optical axis direction, it is possible to vary theeffective operation length of the thermal react material such asbimetallic sheet in response to the projection magnification. Thus, itbecomes possible to set the correction amount corresponding to theprojection magnification. Specifically, the projection TV set apparatushaving one kind of lens can be applied to devices having differentscreen sizes.

According to the present invention, since there are provided the twoguide slots and the other end of the thermal react material such asbimetallic sheet is sandwiched between the two guide members, thedisplacement of the thermal react material such as bimetallic sheet canbe smoothly transmitted to the inner tube and the inner tube can easilybe displaced in the optical axis direction.

According to the present invention, there is provided the lens focuscorrection device in which the two guide slots are defined on the outerperipheral wall portion of the outer tube, the slide portion is disposedin one guide slot and the guide member integrally formed with the innertube is engaged with the other guide slot, the displacement of thethermal react material such as bimetallic sheet in the circumferentialdirection can easily be transmitted to the inner tube. Therefore, itbecomes possible to correct the focus position.

According to the present invention, since the positions at which thethermal react materials such as bimetallic sheet are fixed to the slideportion can be adjusted and the effective operation length of thethermal react material such as bimetallic sheet can continuously bevaried, it becomes possible to correct the focus position changed due tounexpected elements other than expansion and contraction of the tube,i.e., the focus position changed in accordance with so-called lenstemperature change circumstances.

Further, according to the present invention, it is possible to correctthe focus position in response to the change of the projectionmagnification and the temperature change circumstances.

Further, according to the present invention, since the thermal reactmaterial such as bimetallic sheet are formed of the bimetals, it ispossible to provide the sample lens focus correction device with ease.

Furthermore, since the optical lenses are held within the inner tube, itis possible to correct the focus position by displacing the inner tubein the optical axis direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an arrangement of an example of arear projector according to the related art;

FIG. 2 is a schematic diagram showing an arrangement of an example of alens device according to the related art;

FIG. 3 is a graph showing a relationship between a conduction time ofthe rear projector after the rear projector is energized and a lensfocus position moved amount according to the related art;

FIG. 4 is a schematic diagram showing an arrangement of a lens focusposition correction device for use with a projector according to anembodiment of the present invention;

FIG. 5 is a plan view showing a main portion of the lens focuscorrection device shown in FIG. 4;

FIG. 6 is a schematic diagram of a main portion used to explain the lensfocus correction device shown in FIG. 4;

FIG. 7 is a plan view showing a main portion of a projector lens focuscorrection device according to a second embodiment of the presentinvention;

FIG. 8 is a cross-sectional view showing a main portion of a projectorlens focus correction device according to a third embodiment of thepresent invention;

FIG. 9 is a partly cross-sectional plan view showing a main portion ofthe projector lens focus correction device shown in FIG. 8;

FIG. 10 is a partly cross-sectional plan view showing a main portion ofa projector lens focus correction device according to a fourthembodiment of the present invention;

FIG. 11 is a plan view showing a main portion of a projector lens focuscorrection device according to a fifth embodiment of the presentinvention;

FIG. 12 is a cross-sectional view showing a projector lens focuscorrection device according to a sixth embodiment of the presentinvention;

FIG. 13 is a plan view of the projector lens focus correction deviceshown in FIG. 12;

FIG. 14 is a cross-sectional view showing a projector lens focuscorrection device according to a seventh embodiment of the presentinvention;

FIG. 15 is a plan view of the projector lens focus correction deviceshown in FIG. 14;

FIG. 16 is a cross-sectional view showing a projector lens focuscorrection device according to an eighth embodiment of the presentinvention; and

FIG. 17 is a plan view of the projector lens focus correction deviceshown in FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A lens focus correction device according to the embodiments of thepresent invention will now be described in detail with reference to thedrawings. In FIG. 4 and the following sheets of drawings, like partscorresponding to those of FIGS. 1 and 2 are marked with the samereference numerals and therefore need not be described in detail.

FIG. 4 shows a lens focus correction device according to an embodimentof the present invention. In FIG. 4, reference numeral 2 2R, 2G, 2B!designates the three-tube color cathode ray tube for a rear projector.Reference numeral 31 depicts a projection lens apparatus integrallyattached to the front surface of the panel of the cathode ray tube 2.The projection lens apparatus 31 includes a lens focus correctionfunction according to the present invention.

The cathode ray tube 2 uses the liquid-cooling tube in which theliquid-cooling liquid 8 is filled into the space formed by the panelfront surface, the curvature of field correction lens 7 and the sealingframe 9.

As shown in FIG. 4, the projection lens apparatus 31 is fixed to thecathode ray tube 2 by fixing an outer tube 33 constructing the tube 32to the sealing frame 9 of the cathode ray tube 2 side by some suitablemeans, such as the screws 11 or the like. At that time, the curvature offield correction lens 7 is sandwiched between the sealing frame 9 andthe outer tube 33. In FIG. 4, reference numeral 14 depicts a partitionplate.

The tube 32 is comprised of the outer tube 33 and an inner tube 34rotatably provided within the outer tube 33 so as to become movablealong the optical axis C direction. The inner tube 34 includes aplurality of optical lenses 15, 16, 17 and 7 arranged therein. Theoptical lenses 15, 16, 17 and 7 constitute the main lens group 3.

The inner tube 34 includes on its front and rear end portions slidingcontact portions 35 which are brought in contact with the innerperipheral surface of the outer tube 33 to support the inner tube 34 sothat the inner tube 34 becomes rotatable and slidable along the opticalaxis C direction.

The outer tube 33 has on its outer peripheral wall portion defined twogrooves, i.e., guide slots 37, 38 intersecting the optical axis Cdefined from a plane standpoint. To one guide slot 37 are engaged twoguide members (40A, 40B) (see FIG. 5) which are integrally extended fromthe outer peripheral wall portion of the inner tube 34.

To the other guide slot 38 is disposed a slide portion 41 which canslide along the guide slot 38. The slide portion 41 comprises a narrowportion and a wide portion. The narrow portion is inserted into theguide slot 38 and a stepped surface formed by the narrow portion and thewide portion is brought in contact with the inner surface of the outertube 33.

The slide portion 41 has a fastening means, e.g., thumbscrew 43 fittedinto its narrow portion through a spacer 42 which comes in contact withthe outer surface of the outer tube 33. Under the condition that thethumbscrew 43 is fastened, the stepped surface of the slide portion 41and the spacer 42 are forced against the outer tube 33 and thereby fixedto the outer tube 33. When the thumbscrew 33 is loosened, the steppedsurface of the slide portion 41 and the spacer 42 are released frombeing fixed to the outer tube 33 and can be moved along the guide slot38.

On the other hand, a plate-shaped thermal react material such asbimetallic sheet, e.g., bimetal 45, is disposed between the outer tube33 and the inner tube 34 along the optical axis C direction. One end ofthe bimetal 45 is fixed by fixing means, e.g., screw 46, to the wideportion of the slide portion 41 and the other end thereof is sandwichedbetween the two guide members 40A and 40B.

The two guide slots 37 and 38 are inclined at a predetermined angle θfrom the lens optical axis C in the vertical direction as shown in FIG.5, for example. The angle θ is set in response to the numerical apertureand the focal length of the projection apparatus 31 and a correctionamount of the bimetal 45 and can be set to several degrees, for example.

The outer tube 33 and the inner tube 34 constructing the tube 32 areeach made of resin, for example.

Of the main lens group 3 formed of four lenses, the second optical lens16 is formed of a glass lens and other first, third and fourth opticallenses 15, 16 and 7 are formed of plastic lenses.

In FIG. 4, the bimetal 45, the slide portion 41 having the thumbscrew43, the guide members 40A, 40B integrally formed with the inner tube 34and the two guide slots 37, 38 defined on the outer tube 33 constitute amain lens focus correction mechanism.

With the above-mentioned arrangement, in order to properly focus thelens at room temperature, the guide members 40 (40A, 40B) engaged at thetip end of the bimetal 45 fixed to the slide portion 41 are moved alongthe oblique guide slot 37 by moving the slide portion 41 along theoblique guide slot 38 under the condition that the thumbscrew 43 isloosened. Then, the focus position is adjusted by moving the inner tube34 integrally formed with the guide members 40 (40A, 40B) along the lensoptical axis C direction while the inner tube 34 is being rotated. Afterthe focus position has been adjusted, the thumbscrew 43 is tightened andthe slide portion 41 is fixed to the outer tube 33. Thus, the lens focusposition is fixed.

FIG. 5 shows a positional relationship between the guide members 40A,40B and the bimetal 45 under the condition that the lens focus positionis determined at room temperature. As shown in FIG. 5, the bimetal 45 isdisposed in the direction substantially perpendicular to the guide slot37 of the outer tube 33 and placed in the straight line state.

After the projection TV set apparatus having the cathode ray tube 2 isenergized, when a temperature rises with a time to expand the tube,particularly, the outer tube 33, by heat so that the lens focus positionis changed from the initially adjusted lens focus position, as shown inFIG. 6, the bimetal 45 is changed, i.e., the bimetal 45 is curved fromthe straight line state shown in FIG. 5, thereby lowering the guidemembers 40 (40A, 40B) in the lower direction of FIG. 6. As a result, theinner tube 34 is rotated and this rotational displacement of the innertube 34 is transmitted along the guide slot 37 and thereby converted tothe displacement of the optical axis C direction. Consequently, theinner tube 34 is moved toward the cathode ray tube 2 side (i.e., in theright-hand direction in FIGS. 6 and 4) to change the spacing between themain lens group 3 and the cathode ray tube 2, thereby the lens focusposition being corrected, i.e., the lens focus position being returnedto the initial focus position set at room temperature. In FIG. 6,reference symbol d₁ depicts an amount in which the inner tube 34 ismoved when the focus position is corrected.

In the example shown in FIGS. 5 and 6, since the two guide slots 37 and38 are formed in parallel to each other, regardless of the position atwhich the guide members 40 (40A, 40B) are disposed in the guide slot 37,a distance between the fixed portion and the action point of the bimetal45, i.e., the effective action length is not changed but is keptconstant. Accordingly, even though the position of the optical axisdirection of the inner tube 34 is displaced a little when the focusposition is initially adjusted, it is possible to set a constantcorrection amount. Further, when the projection magnification is variedby changing the initial focus adjustment position, it is possible to seta constant correction amount regardless of the projection magnification.Specifically, when the projection magnification is constant or theprojection magnification lies in a narrow range (e.g., 46-inch to48-inch), the correction amount is not changed depending on theadjustment position and the projection apparatus is easy to handle.

FIG. 7 shows a lens focus correction device according to a secondembodiment of the present invention.

A focus position correction amount tends to increase when a projectionmagnification is large and tends to decrease when a projectionmagnification is small. According to this embodiment, the focus positioncorrection amount can cope with the projection magnification.

FIG. 7 shows only the focus position correction mechanism including theguide slots defined in the outer tube 33. A rest of arrangements issimilar to that of FIG. 4 and therefore need not be described in detail.

According to this embodiment, as shown in FIG. 7, at least one of theguide slots 37 is inclined at a predetermined angle θ with respect tothe lens optical axis C in the vertical direction similarly as describedabove so that the two guide slots 37 and 38 are not made parallel toeach other. In this embodiment, the guide slot 38 which guides the slideportion 41 is made perpendicular to the optical axis C and the guideslot 37 which guides the guide members 40 (40A, 40B) is inclined at thepredetermined angle θ with respect to the optical axis C.

The predetermined angle θ is set in response to the focal length, thecorrection amount of the bimetal 45 or the like. By way of example, whenthe numerical aperture of the main lens group 3 is 100 mm, the focallength is 77 mm and the length of the bimetal 45 is 50 mm, an inequalityof 0°<θ≦10° is satisfied. The predetermined angle θ should preferably beset to several degrees, e.g., about 5°.

In FIG. 7, when the guide members 40 (40A, 40B) are placed at a solidline position b, the projection lens apparatus 31 is set to the focusadjustment position of magnification with which an image is projectedonto a 46-inch screen, for example. When the guide members 40 (40A, 40B)are placed at a two-dot chain line c position, the projection lensapparatus 31 is set to the focus adjustment position of magnificationwith which an image is projected onto a 41-inch screen. When the guidemembers 40 (40A, 40B) are placed at a two-dot chain line a position, theprojection lens apparatus 31 is set to the focus adjustment position ofmagnification with which an image is projected onto 53-inch screen.

With the above-mentioned arrangement, since the length of the bimetal 45is constant, a point (action point) in which the bimetal 45 contactswith the guide member is changed in response to the focus adjustmentposition changed by the change of the screen size, whereby the effectiveaction length of the bimetal 45 is changed. Specifically, as the screensize becomes small (see two-dot chain line and solid line in FIG. 1),the effective action length of the bimetal 45 is reduced as shown by L₃,L₂, L₁ in FIG. 7, in that order, and the correction amount is reducedaccordingly. As a consequence, it is possible to automatically changethe correction amount of the focus position in response to theprojection magnification.

Furthermore, according to this embodiment, it is possible to cope withpreviously-calculated elements for changing the focus position, such asexpansion and contraction of a cathode ray tube set assembly other thanthe expansion and contraction of the outer tube 33 through a range oftemperatures. Therefore, one kind of the projection lens apparatus 31can be applied to rear projectors with different screen sizes in use.

FIGS. 8 and 9 show a lens focus correction device according to a thirdembodiment of the present invention.

FIG. 8 is a cross-sectional view and FIG. 9 is a plan view each showingonly the focus position correction mechanism according to the presentinvention. In FIGS. 8 and 9, other arrangements are similar to those ofFIG. 4 and therefore need not be described in detail.

In this embodiment, as shown in FIGS. 8 and 9, the outer tube 33 has onits outer peripheral wall portion the two oblique parallel guide slots37, 38 defined with an inclination of the predetermined angle θ withrespect to the optical axis C. The guide members 40 (40A, 40B) which areintegrally formed with the inner tube 34 are engaged with one guide slot37 and the other guide slot 38 guide the slide portion 41. Anelliptically-elongated aperture 47 is defined in the fixed side of thebimetal 45 and the fixed position of the bimetal 45 can be set in arange of the elliptically-elongated aperture 47 arbitrarily(continuously).

According to the above-mentioned arrangement, by adjusting the fixedposition of the bimetal 45 by the screw 46, it is possible to set theeffective action length of the bimetal 45 in a range of theelliptically-elongated aperture 47 arbitrarily (continuously) as shownby L₄, L₅, L₆ in FIG. 9. Thus, when the focus position change which isbeyond the calculation in the previous design stage occurs at hightemperature, it is possible to correct the focus position only bychanging the fixed position without changing the guide slots 37, 38 ofthe outer tube 33.

Therefore, this embodiment can cope with elements other than theexpansion and contraction of the outer tube 33. Specifically, it ispossible to adjust the correction amount in response to the temperaturechange circumstances of the lens by previously setting bimetalcorrection coefficient in response to unpredictable circumstances inwhich the lens focus is changed with temperature (temperature change isdifferent depending on individual characteristics even when the size ofequipment is the same).

FIG. 10 shows a lens focus correction device according to a fourthembodiment of the present invention. FIG. 10 shows only the focusposition correction mechanism. In FIG. 10, other arrangements aresimilar to those of FIG. 7 and therefore need not be described indetail.

According to this embodiment, the lens focus correction device is formedof a combination of the lens focus correction devices shown in FIGS. 7and 9. Specifically, as shown in FIG. 10, on the outer peripheral wallportion of the outer tube 33 are formed the two guide slots 37, 38 underthe condition that at least one guide slot 37 is inclined at thepredetermined angle θ with respect to the lens optical axis C in thevertical direction so that the two guide slots 37 and 38 are not made inparallel to each other. In this embodiment, the guide slot 38 whichguides the slide portion 41 is made perpendicular to the optical axis Cand the guide slot 37 which guides the guide members 40 (40A, 40B) isformed oblique relative to the optical axis C.

On the other hand, the bimetal 47 has the elliptically-elongatedaperture 47 defined in its fixed side. The fixed position of the bimetal45 can be set in a range of the elliptically-elongated aperture 47arbitrarily (continuously).

According to this arrangement, similarly as described above withreference to FIG. 7, by changing the positions of the guide members 40(40A, 40B) in response to the change of the screen size, the effectiveaction length of the bimetal 45 is changed and a correction amountcorresponding to the projection magnification can be obtained. Thus, itis possible to correct the focus position.

Further, it is possible to correct the focus position in response to theunpredictable change of focus position by adjusting the fixed positionof the slide portion 41 of the bimetal 45 in a predetermined range.

Specifically, according to this embodiment, the focus position can becorrected with large freedom as compared with the case of FIGS. 7 and 9.Therefore, this embodiment can cope with the predictable change of thefocus position and the unpredictable change of the focus positionwithout varying the design and assembly parts.

FIG. 11 shows a lens focus correction device according to a fifthembodiment of the present invention. FIG. 11 shows only the focusposition correction mechanism. In FIG. 11, other arrangements aresimilar to those of FIG. 4 and therefore need not be described indetail.

According to this embodiment, as shown in FIG. 11, the outer tube 33includes on its outer peripheral wall portion defined a guide slot 51with an inclination of a predetermined angle θ with respect to theoptical axis C in the vertical direction. The slide portion 41 and theguide members 40 (40A, 40B) which are integrally formed with the innertube 34 are guided into the guide slot 51. As a bimetal, there isprovided a U-shaped bimetal 52 whose one end is fixed to the slideportion 41 by the screw 46. The other end of the bimetal 52 issandwiched between the two guide members 40A and 40B.

With the above-mentioned arrangement, after the initial focus positionis adjusted through the slide portion 41 and the slide portion 41 isfixed to the outer tube 33 by the thumbscrew 43, if a temperature ischanged due to conduction or the like, then the U-shaped bimetal 52 isdisplaced in the opening direction, for example, as shown by a one-dotchain line in FIG. 11 so that the guide member 40 engaged with the otherend of the bimetal 52 is moved along the guide slot 51. Therefore, theinner tube 34 is moved along the lens optical axis C to the right-handside of FIGS. 4 and 11, thereby making it possible to correct the focusposition.

Also in this case, though not shown, if the fixed position of thebimetal 52 is arbitrarily set within a predetermined range similarly toFIG. 9, then the present invention can cope with the unpredictablechange elements of the focus position without varying the design andassembly parts.

Furthermore, according to this embodiment, it is possible to increasethe effective action length and the correction amount by the U-shapedbimetal 52.

FIGS. 12 and 13 show a lens focus correction device according to a sixthembodiment of the present invention. FIGS. 12 and 13 show mainly thefocus position correction mechanism and other arrangements are similarto those of FIG. 4. In FIGS. 12 and 13, like parts corresponding tothose of FIG. 4 are marked with the same references and therefore neednot be described in detail.

According to this embodiment, the outer tube 33 has on its outerperipheral wall portion two guide slots 54 and 55 defined with aninclination of the predetermined angle θ with respect to the lensoptical axis C in the vertical direction similarly as described above.The guide slots 54 and 55 are formed on axes which are parallel to eachother.

One guide member 56 which is integrally formed with the inner tube 34 isengaged with one guide slot 54 and the slide portion 41 is guided intothe other guide slot 55. The slide portion 41 has the thumbscrew 43fitted thereto through a spacer.

A band-shaped bimetal 58 is disposed between the outer tube 33 and theinner tube 34 so as to extend along the inner peripheral direction ofthe outer tube 33. One end of the bimetal 58 is fixed to the slideportion 41 by the screw 46, for example, and the other end thereof isfixed to the guide member 56. The band-shaped bimetal 58 is disposed inan annular fashion and may be wound in a range of from 270° to 360°, forexample, according to this embodiment.

With the above-mentioned arrangement, after the slide portion 41 ismoved along the guide slot 55 and the inner tube 34 which is integrallyformed with the guide member 56 is moved in the optical axis C directionthrough the bimetal 58 to thereby adjust the initial focus position, theslide portion 41 is fixed to the outer tube 33 through the thumbscrew43. When the outer tube 33 is expanded by heat to change the focusposition after the temperature is changed by conduction or the like, theband-shaped bimetal 58 disposed in an annular fashion is displaced inthe direction in which a diameter is reduced with the result that theother end of the bimetal 58 is moved in the circumferential direction ofthe outer tube 33. Thus, while rotating, the inner tube 34 fixed to theother end of the bimetal 58 is moved through the guide member 56 in thelens optical axis C direction, i.e., in the right-hand side direction ofFIGS. 13 and 4, thereby making it possible to correct the focusposition. Since the guide slots 54, 55 are disposed on the parallelaxes, the effective action length of the bimetal 58 can be kept constantregardless of the focus adjustment position.

According to this embodiment, it is possible to increase the effectiveaction length, accordingly, to increase the correction amount bydisposing the band-shaped bimetal 58 along the inner circumferentialdirection of the outer tube 33 in an annular fashion.

FIGS. 14 and 15 show a lens focus correction device according to aseventh embodiment of the present invention. In this embodiment, theband-shaped bimetal 58 described hereinbefore with reference to FIGS. 12and 13 is disposed with a wrapping angle of 360° or greater.

In this arrangement, the effective action length of the bimetal 58 canbe increased more and there can be obtained a larger correction amount.Also in this case, the effective action length of the bimetal 58 can beheld constant regardless of the focus adjustment position.

FIGS. 16 and 17 show a lens focus correction device according to aneighth embodiment of the present invention. In this embodiment, theband-shaped bimetal 58 described above with reference to FIGS. 12 and 13is disposed with a wrapping angle smaller than 360°, e.g., 180°.Accordingly, guide slots 54 and 55 defined in the outer peripheral wallportion of the outer tube 33 are formed in a positional relationship inwhich they are opposed at an angular extent of 180°. In this case, thetwo guide slots 54 and 55 can be formed on the same axis or on theparallel axes.

With the above-mentioned arrangement, when a temperature is changed, theother end of the bimetal 58 fixed to the guide member 56 is moved in thecircumferential direction so that the inner tube 34 can be displaced bythe oblique guide slot 54 in the lens optical axis C direction whilebeing rotated, thereby making it possible to correct the focus position.Also in this case, the effective action length of the bimetal 58 can beheld constant regardless of the focus adjustment position.

In the examples shown in FIGS. 12, 14 and 16, the band-shaped bimetal 58is disposed along the circumferential direction of the outer tube 33,though not shown. Therefore, if the fixed position of the bimetal 58relative to the slide portion 41 can be arbitrarily set in apredetermined range similarly as described above with reference to FIG.9, then it is possible to correct the lens focus position in response tothe temperature change circumstance.

As described above, according to this embodiment, in the rear projector,it is possible to correct the change between the focus positionpresented immediately after the projector is energized and the focusposition presented after the tube 33 is expanded by heat at a timingpoint in which a temperature within the apparatus is raised by heatgenerated from the circuit or the cathode ray tube 2 after the projectoris energized by the bimetals 45, 52 or 58 in the opposite direction.Thus, regardless of duration of conduction, it is possible to maintainan image of high quality after the conduction has been started.

Further, it is possible to reduce restriction conditions of lens design,such as to hold the moving amount of the focus position within apredetermined range when a temperature is changed or the like. Thus,freedom in designing the lens can be increased. Therefore, it ispossible to reduce cost as compared with the conventional design methodand to improve efficiency. In particular, the rear projector iscomprised of many plastic lenses which are easily affected by theinfluence of temperature as compared with the glass lens. As a result,advantages involving cost and efficiency, such as reduction of lensesand improvement of productivity can be made sufficiently large.

On the rear projector production line, the rear projector iscontinuously energized until the process for adjusting the focusposition. However, the rear projector is continuously energized during arest or a period in which the production line is stopped by a problem orthe like with the result that the conduction time before the focusadjustment process is not constant. However, according to thisembodiment, it is possible to maintain the image of high picture qualityinitially set by correcting the focus position moved by a fluctuation oftemperature when the rear projector is assembled and adjusted, i.e., thetemperature change due to difference of conduction time regardless of aduration of conduction time.

While the bimetal is used as the thermal react material such asbimetallic sheet as described above, the present invention is notlimited thereto and a shape memory material or the like can be usedtherefor.

While the present invention is applied to a projection lens of the rearprojector or the like as described above, the present invention is notlimited thereto and can be applied to a projection lens system of areflection type projector, a liquid crystal projector and otherapparatus which are affected by a temperature change.

While the focus position changed by the expansion of the tube 32 by heatis corrected by moving the inner tube 34 to the right-hand side in FIG.4, i.e., toward to the cathode ray tube 2 side by the bimetal 45, 52 or58 as described above, the present invention is not limited thereto andthe focus position changed by other causes, such as expansion of thecabinet by heat or the like, can be corrected by moving the inner tube34 to the left-hand side in FIG. 4, i.e., to the opposite side of thecathode ray tube 2.

While there is provided one bimetal 45 as shown in FIG. 4, the presentinvention is not limited thereto and a plurality of laminated bimetalscan be used when necessary, e.g., to increase action force.

While one focus position correction mechanism is provided as describedabove, the present invention is not limited thereto and it is possibleto provide a plurality of focus position correction mechanisms of thesame arrangement.

According to the present invention, even when the lens focus position ischanged as the tube expands and contracts due to temperature change, thelens focus position can automatically be corrected by the thermal reactmaterial such as bimetallic sheet, thereby maintaining the initial focusposition.

According to the present invention, since the rotational displacement ofthe inner tube can be converted by the oblique guide through-hole intothe displacement of the optical axis, it is possible to correct the lensfocus position by converting the displacement of the thermal reactmaterial such as bimetallic sheet into the optical axis directiondisplacement of the inner tube.

According to the present invention, since the thermal react materialsuch as bimetallic sheet is disposed along the optical axis direction,when the lens focus position is changed due to temperature change, it ispossible to correct the focus position by moving the inner tube alongthe optical axis in the opposite direction while the inner tube is beingrotated by the thermal react material such as bimetallic sheet.

According to the present invention, since the thermal react materialsuch as bimetallic sheet is disposed along the inner peripheraldirection of the outer tube, even when the lens focus position ischanged due to temperature change, it is possible to correct the focusposition by moving the inner tube along the optical axis in the oppositedirection while the inner tube is being rotated by the thermal reactmaterial such as bimetallic sheet. Moreover, in this case, the effectiveoperation length of the thermal react material such as bimetallic sheetis increased and it is therefore possible to increase the correctionamount.

According to the present invention, since the thermal react materialsuch as bimetallic sheet is U-shaped, when the lens focus position ischanged due to temperature change, it is possible to correct the focusposition by moving the inner tube along the optical axis in the oppositedirection while the inner tube is being rotated by the thermal reactmaterial such as bimetallic sheet. Also in this case, the effectiveoperation length of the thermal react material such as bimetallic sheetis increased and it is therefore possible to increase the correctionamount.

According to the present invention, since the guide slot for guiding theslide portion and the guide slot for guiding the guide member are formedin parallel to each other, it is possible to keep the effectiveoperation length of the thermal react material such as bimetallic sheetconstant at any focus adjustment position.

According to the present invention, since the guide slot for guiding theslide portion and the guide slot for guiding the guiding member areformed parallel to each other, it is possible to vary the effectiveoperation length of the thermal react material such as bimetallic sheetin response to a shooting magnification. Therefore, the projection TVset apparatus having one kind of lens system can be applied to deviceshaving different screen sizes.

According to the present invention, since the other end of the thermalreact material such as bimetallic sheet is sandwiched between the twoguide members, the change of the thermal react material such asbimetallic sheet is smoothly transmitted to the inner tube through theguide member. Thus, it becomes possible to correct the focus position.

According to the present invention, since the lens focus correctiondevice in which the band-shaped thermal react material such asbimetallic sheet is disposed along the circumferential directionincludes the two guide slots defined on the outer peripheral wallportion of the outer tube to guide the slide portion and the guidemember, the initial focus adjustment position can be set and the changeof the focus position due to the temperature change can be corrected.

According to the present invention, since the position at which thethermal react material such as bimetallic sheet is fixed to the slideportion can be adjusted, the effective operation length of the thermalreact material such as bimetallic sheet can be set arbitrary within apredetermined range and the present invention can cope with thetemperature change circumstance of lenses.

Moreover, according to the present invention, it is possible to correctthe focus position in response to the projection magnification and thetemperature change circumstance.

Further, according to the present invention, since the thermal reactmaterial such as bimetallic sheet is formed of the bimetal, it ispossible to provide the lens focus correction device of simplearrangement with ease.

Furthermore, according to the present invention, since the optical lensis held within the inner tube, it is possible to correct the lens focusposition by moving the inner tube.

Accordingly, when the present invention is applied to the projectiontype image display apparatus such as a projector or the like, the focusposition presented immediately after the conduction and the focusposition changed when the tube is expanded by heat due to thetemperature change after conduction can be corrected in the oppositedirection by the thermal react material such as bimetallic sheet.Therefore, it is possible to maintain the image of high definition setafter conduction has started.

Further, since lens design restricting conditions, such as to suppressthe moving amount of the focus position due to the change of temperaturewithin a predetermined range can be reduced and lens design freedom canbe increased, it can be expected to reduce the cost and to enhance theperformance as compared with the conventional design method. Inparticular, since the projector type image display apparatus uses manyplastic lenses that are easily affected by the temperature as comparedwith the glass lens, the present invention has many advantages involvingcost and performance, such as reduction of the number of lenses and toimprove productivity or the like as compared with other lens systems.

Furthermore, since the temperature fluctuation (displacement of focusposition due to temperature change caused by conduction time difference)occurs when the projector type image display device is assembled andadjusted is corrected, it is possible to maintain the initial image ofhigh definition regardless of duration of conduction time.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to those precise embodiments and that various changes andmodifications could be effected therein by one skilled in the artwithout departing from the spirit or scope of the invention as definedin the appended claims.

What is claimed is:
 1. A lens automatic focus correction devicecomprising:a lens having an optical axis; an outer tube; an inner tubearranged within said outer tube for supporting said lens; and abimetallic sheet disposed substantially along a direction of saidoptical axis, said bimetallic sheet having a first end thereof fixed toa slide portion provided in said outer tube and a second end thereofengaged with a guide member integrally formed with said inner tube, saidbimetallic sheet moving said inner tube relative to said outer tubealong said optical axis direction in response to a change intemperature, wherein said outer tube has an oblique guide slot formed ina wall portion thereof and said oblique guide slot converts a rotationaldisplacement of said inner tube to a linear displacement thereof alongsaid optical axis direction, and a thumbscrew fixes said slide portionto said outer tube when a focus position of said lens has been adjusted.2. A lens automatic focus correction device comprising:a lens having anoptical axis; an outer tube; an inner tube arranged within said outertube for supporting said lens; and a bimetallic sheet moving said innertube relative to said outer tube along a direction of said optical axisin response to a change in temperature, wherein said outer tube has afirst guide slot formed in a wall portion thereof, said first guide slotinclined at a predetermined angle with respect to said optical axis,said outer tube has a second guide slot formed in a wall portionthereof, said second guide slot positioned substantially perpendicularto said optical axis such that said first and second guide slots are notmutually parallel, and said bimetallic sheet has a first end thereoffixed to a slide portion provided in said second guide slot and a secondend thereof engaged with a guide member integrally formed with saidinner tube, said guide member engaging said first guide slot.
 3. A lensautomatic focus correction device comprising:a lens having an opticalaxis; an outer tube; an inner tube arranged within said outer tube forsupporting said lens; and a bimetallic band moving said inner tuberelative to said outer tube along a direction of said optical axis inresponse to a change in temperature, wherein said outer tube has firstand second guide slots formed in a wall portion thereof, said first andsecond guide slots inclined at a predetermined angle with respect tosaid optical axis, and said bimetallic band extends along an innerperiphery of said outer tube and is disposed between said outer tube andsaid inner tube, said bimetallic band having a first end thereof fixedto a slide portion provided in said second guide slot and a second endthereof engaged with a guide member integrally formed with said innertube for engaging said first guide slot.
 4. A lens automatic focuscorrection device according to claim 3, wherein said bimetallic bandwraps around said inner tube through an angle of greater than 360°.
 5. Alens automatic focus correction device according to claim 3, whereinsaid bimetallic band wraps around said inner tube through an angle ofbetween about 180° and 360°.